Lamp design

ABSTRACT

An improved support is provided for locating a lamp filament axially within a lamp sleeve. The illustrated support is a spiral coil that includes a small diameter center portion that makes contact with the filament. On either side of the filament-contacting portion, the coil opens up to larger diameters for contacting the inner wall of the quartz sleeve within which the filament is housed. The support thus appears H-shaped when viewed from the side. A lamp filament is also provided with expansion compensation sections at either end of a central section. The filament wire in the compensation sections is wound into coils having a greater diameter and also a greater spacing between windings, as compared to coil in the central section. The expansion compensation sections are preferably capable of compressing and thereby absorbing thermal expansion of the filament during operation, without shorting the filament across adjacent windings.

REFERENCE TO RELATED APPLICATION

[0001] The present application is a continuation-in-part of U.S.application Ser. No. 10/179,658, filed Jun. 24, 2002, and claimspriority under 35 U.S.C. §119(e) to U.S. provisional patent applicationNo. 60/301,339, filed Jun. 27, 2001 (attorney docket no. ASMEX.341PR)and to U.S. provisional patent application No. 60/370,099 filed Apr. 3,2002 (attorney docket no. ASMEX.394PR).

FIELD OF THE INVENTION

[0002] The invention relates to lamp filaments generally and, moreparticularly, to improving support and design of filaments for highenergy, radiantly heated semiconductor processing reactors.

BACKGROUND OF THE INVENTION

[0003] Chemical vapor deposition (CVD) is a very well known process inthe semiconductor industry for forming thin films of materials onsubstrates and silicon wafers. In a CVD process, gaseous molecules ofthe material to be deposited are supplied to wafers to form a thin filmof that material on wafers by chemical reaction. Such formed thin filmsmay be polycrystalline, amorphous or epitaxial. Typically, CVD processesare conducted at elevated temperatures to accelerate a chemical reactionand to produce high quality films. Some processes, such as epitaxialsilicon deposition, are conducted at extremely high temperatures (>900°C.).

[0004] Substrates (e.g., silicon wafers) can be heated using resistanceheating, induction heating or radiant heating. Among these, radiantheating is the most efficient technique and, hence, is the currentlyfavored method for certain types of CVD. Radiant heating involvespositioning infrared lamps within high-temperature ovens, calledreactors. Typically these lamps comprise metal filaments within a quartzor other transparent sleeve. A quartz wall also separates the reactionchamber from the lamps. A susceptor within the reaction chambertypically supports a single substrate and also absorbs the radiantenergy to help uniformly heat the wafer.

[0005] One arrangement of a radiantly heated reactor is shown in U.S.Pat. No. 4,975,561, issued Dec. 4, 1990 to Robinson et al., thedisclosure of which is incorporated herein by reference. In thatdisclosure, linear infrared lamps are arranged in a pair of crossingarrays, with one orientation above the lamps and an orthogonalorientation below the susceptor. The grid resulting from the crossingarray configuration facilitates some control over the temperatureuniformity of the wafer by adjusting the power that is delivered to anyparticular lamp or group of lamps. Additional spot lamps are alsoemployed in the disclosed system of the '561 patent.

[0006] During a CVD process, one or more substrates are placed on awafer support inside a chamber formed within the reactor (i.e., thereaction chamber). Both the wafer and the support are radiantly heatedto a desired temperature, while the radiant energy passes through thequartz sleeve and quartz chamber walls such that they remain relativelycool. Accordingly, the reactor is called a “cold-wall” reactor. Only thewafer (and some supporting elements like the susceptor) are heated tothe temperature sufficient to activate the reaction gases. In a typicalwafer treatment step, reactant gases are passed over the heated wafer,causing the chemical vapor deposition (CVD) of a thin layer of thedesired material on the wafer.

[0007] Radiant heat can likewise be employed for any of a number ofother processes in semiconductor fabrication, including, withoutlimitation, etching, dopant diffusion, dopant activation, oxidation,nitridation, silicidation, reorientation anneals, oxide or metal reflow,etc. Furthermore, the heating system of the '561 patent is exemplaryonly; many other radiant heating systems are known in the art.

[0008] One problem with currently available radiant heating elements isthat the lifespan of the lamps is short, causing significant downtimefor frequent replacement. Extended use of such lamps, typicallyincluding repeated cycling as wafers are sequentially loaded, processedat high temperature and unloaded, leads to lamp failure.

[0009] Accordingly, a need exists for a system for improving lamplifespan.

SUMMARY OF THE INVENTION

[0010] In accordance with one aspect of the invention, a lamp filamentsupport is provided with a filament-contacting portion and at least twosleeve-contacting portions. In the illustrated embodiment, thefilament-contacting portion is provided between two sleeve-contactingportions, resembling an H-shaped element in side view.

[0011] In accordance with another aspect of the invetion, a lamp isprovided with a transparent sleeve having an inner diameter D. Afilament is housed within and extends axially along the transparentsleeve. A plurality of filament supports radially space the filamentfrom an inner surface of the transparent sleeve. The filament supportsinclude a plurality of axially spaced pairs of sleeve-contactingportions. Adjacent sleeve-contacting portions of the pairs are axiallyspaced by a distance L, wherein a ratio of L/D for each pair is betweenabout 0.5 and 1.25.

[0012] In accordance with another aspect of the invention, a filamentsupport is provided for radially spacing a lamp filament from atransparent lamp sleeve. The filament support includes a firstsleeve-contacting portion and a second sleeve-contacting portion spacedfrom the second sleeve-contacting portion. A filament-contacting portionis connected to the first and second sleeve-contacting portions.

[0013] In accordance with another aspect of the invention, a lampfilament is provided with expansion compensation sections at either endof the central section. The compensation sections have a greaterdiameter about the filament axis, as compared to the central section,and also have greater spacing between windings. The compensationsections are preferably capable of compressing and absorbing thermalexpansion of the filament during operation, without shorting thefilament across adjacent windings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other aspects of the invention will be readily apparentfrom the description below and the appended drawings, in which likereference numerals refer to similar parts throughout, which are meant toillustrate and not to limit the invention, and in which:

[0015]FIG. 1 is a side view of a typical lamp with a conventionalfilament support.

[0016]FIG. 2 is a side view of a typical lamp illustrating the problemof shorting caused by rotation of the support and sagging of thefilament.

[0017]FIG. 3 is a side view of a filament support used in conjunctionwith a dimpled lamp sleeve.

[0018]FIG. 4 is an enlarged view showing two supports which hold afilament away from a lamp tube wall, constructed in accordance with apreferred embodiment of the present invention

[0019]FIG. 5 is a side view of a tubular lamp having a plurality ofsupports, constructed in accordance with a preferred embodiment of thepresent invention.

[0020]FIG. 6 is a schematic side view of a lamp, for purposes ofillustrating the effect of thermal expansion upon the lamp filament.

[0021]FIG. 7 is a schematic side view of one end of a lamp provided withthermal compensation sections, in accordance with another embodiment ofthe present invention.

[0022]FIG. 8 is a schematic side view of a lamp employing thermalexpansion compensation sections at both ends, for purposes ofillustrating the operation of the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] FIGS. 1-5 illustrate sections of lamps for purposes of describingproblems and solutions with respect to filament support. FIGS. 6-8illustrate lamps for purposes of describing problems and solutions withrespect to filament expansion and contraction.

[0024] The material of a lamp filament used in radiant heatingapplications is typically tungsten wire, which does not maintain itsstiffness at high temperatures. Conventionally, additional spiralsupport wires, each having a spiral or conical shape, are added aroundthe filament periodically along the filament length to help support thefilament, as shown in FIGS. 1-3.

[0025]FIG. 1 depicts a quartz lamp 12 as might be typically found in areactor. The quartz lamp 12 comprises a filament 14, spiral filamentsupport 16 and quartz sleeve 18. The support 16 contacts the filament 14at an inner part of its spiral, and buttresses against the quartz sleeve18 at an outer part of the spiral. Thus, the support 16 is intended tohold the filament 14 away from the quartz sleeve 18 of the lamp 12.Unfortunately, this support has been found to tip under operation.

[0026]FIG. 2 is a side view of a typical lamp 12 illustrating theproblem of shorting caused by rotation of the support 16 and sagging ofthe filament 14. As electricity passes through the resistive filament14, it begins to glow, and generate heat and light. As the filament 14nears the melting point of the material of which it is made, the hotfilament 14 begins to sag under gravity. This sagging creates a momentload that tends to tip or rotate the support 16, such that it no longerfunctions to hold up the filament 14. As the filament 14 sags, adjacentcoils of the filament 14 grow closer together on the inside curves ofthe deformed filament 14, and eventually create electrical shorts 22, 26along the filament. These shorts 22, 26 in turn allow increasedelectricity to flow through the filament 14, causing its temperature toincrease, and exacerbating the filament sagging problem. Eventually, asthe filament 14 nears the quartz sleeve 18, the heat generated by thefilament begins to blister or melt the quartz, creating a deformation,blister or hole 24. At this point, the integrity of the lamp 12 iscompromised, and it typically fails.

[0027] One proposed solution to this problem has been to “trap” thefilament support 16 by providing dimples 32 in the inner quartz surfaceinto which the support extends, making it more difficult for the supportto rotate out of position. As shown in FIG. 3, however, the support 16still tends to rotate, even with the dimples 32. Furthermore, thedimples 32 are costly to introduce onto the otherwise smooth quartzsleeve 18, and also tend to obscure the otherwise clear quartz, possiblyaffecting radiant heat transmission as well as visual inspection of thelamp 12.

[0028] As shown in FIG. 4, a support 42 constructed in accordance with apreferred embodiment of the present invention includes a plurality ofcontact portions laterally spaced from one another. In the illustratedembodiment, each support 42 comprises two conical spirals, joined attheir apexes. The support 42 comprises one large diameter ring at eitherend, which contacts the quartz sleeve at two sleeve-contacting portions44 and 46, and a series of smaller diameter rings which support thefilament 14 at a filament-contacting portion 47. In the side view ofFIG. 4, the support 42 resembles the letter “H.” However, one skilled inthe art will understand that numerous embodiments may be employed. Forexample, a support resembling the letter “X” in the side view may alsobe used.

[0029] The preferred support 42 comprises tungsten wire having about thesame thickness (e.g., within about ±50% of the thickness) as thefilament 14. While the radially-inward filament-contacting portion 47 ofthe support 42 may get hot during operation, the radially-outwardsleeve-contacting portions 44, 46 tend to be cool enough to avoid damageto the quartz sleeve 18. It will be understood, however, that othermaterials can also be employed in the construction of the support 42.

[0030] As the filament 14 nears the melting point of the material ofwhich it is made, the hot filament 14 begins to sag under gravity. Asshown in FIGS. 1-3, in the prior art, this sagging creates a moment loadthat tends to tip or rotate the support 16, such that it no longerfunctions to hold up the filament 14. However, in the preferredembodiment, the improved support 42 does not tip or rotate under themoment. Advantageously, this prevents the filament from excessivesagging, thereby avoiding shorting and melting the quartz sleeve 18, andconsequently extending the working life of the lamp 12.

[0031] The two sleeve-contacting portions 44, 46 are preferably spacedapart by a distance L. Preferably, the supports are configured such thatL is large enough to minimize the risk of tipping but small enough tominimize risk of sagging of the filament between adjacent contactingportions. Note that risk of sagging is minimized by close spacing Lregardless of whether adjacent sleeve-contacting portions are connected,as with the illustrated embodiment, or are unconnected.

[0032] The preferred spacing L depends upon the height of the supports42, which in turn depends upon the inner diameter D of the quartz sleeve18. Preferably, the support 42 is arranged to have a ratio L/D betweenabout 0.5 and 1.25, more preferably L/D is between about 0.7 and 1.1,and most preferably about 1.0. In an exemplary lamp 12, D=12.7 mm, suchthat the sleeve-contacting portions 44, 46 of the illustrated support 42are preferably between about 6.3 mm and 15.9 mm, more preferably betweenabout 8.9 mm and 14.0 mm, and most preferably about 12.7 mm.

[0033] In the preferred embodiment, the lamp 12 is designed to allow forCVD or other processes typically conducted within a reactor. Inparticular, the filament 14 preferably has at least a 1 kW capacity,more preferably at least a 3 kW capacity, even more preferably at leasta 6 kW capacity and most preferably at least a 10 kW capacity. Inaddition, the reactor (not shown) is preferably capable of achieving atemperature greater than about 500° C., more preferably greater thanabout 700° C. and most preferably greater than about 900° C.

[0034] Referring now to FIG. 5, a lamp 12 is shown with a plurality offilament supports 42 constructed in accordance with a preferredembodiment of the present invention. The supports 42 are spaced alongthe filament 14, thereby holding it within and away from the quartzsleeve 18.

[0035]FIG. 6 depicts a schematic side view of a lamp 12 , illustratingthe effect of thermal expansion upon the lamp filament 14.Conventionally, the filament 14 is rigidly connected to electrodecontacts at the lateral ends of the lamp 12. When the lamp 12 is turnedon, the filament 14 becomes very hot and expands in accordance with itscoefficient of thermal expansion (CTE). As the filament 14 heats up, ittends to expand the most in its center portion, marked “thermalexpansion” in FIG. 6. The rigid connections at the lateral ends of thefilament 14 cause expansion to be absorbed between the closely spacedfilament coils and either end of the filament 14. In particular, theclosely spaced coils within the lateral end zones, marked “compression”in FIG. 6, can become close enough to short out, as described above withrespect to FIG. 3. The shorted coils then exhibit lower resistance andlarger current travels through the filament 14, leading to increasedheat and further filament 14 expansion. When the power to the filament14 is switched off, the filament 14 cools in place and withoutcommensurate contraction. Consequently, through repeated heating andcooling cycles the problem is exacerbated until the filament 14 meltsand the lamp 12 fails.

[0036]FIG. 7 is a schematic side view of an improved lamp 12 providedwith a thermal compensation section of the filament 14, in accordancewith another embodiment of the present invention. While illustrated withthe novel H-shaped supports 42 described above, it will be understoodthat the description of FIGS. 7 and 8 is applicable to filamentssupported by any of a variety of mechanisms.

[0037] The lamp 12 includes a filament 14 supported within a transparentsleeve, preferably comprising quartz. The filament 14 comprises a wireformed of suitable material, and comprises tungsten in the illustratedembodiment. In a central portion 72 of the filament 14, the wire isdensely coiled. This dense coiling causes the filament 14 to heat up andexpand in the central section 72. At either end of the filament 14 is anexpansion compensation section 74. These expansion compensation sections74 are configured to serve as “springs” in the sense that they compressmore readily without shorting, as compared to the central section 72 ofthe filament 14.

[0038] In particular, the expansion compensation sections 74 preferablyare formed by coils having a larger diameter and larger spacing(increased pitch) as compared to the central section 72 of the filament14. Preferably, the diameter of the expansion compensation sections 74is greater than about 1.5 times, and more preferably greater than about2.0 times, that of the coil in the central section 72 of the filament14. Furthermore, the spacing between windings in the expansioncompensation section 74 is preferably greater than about 1.5 times, andmore preferably greater than about 2.0 times, that of the coil in thecentral section 72 of the filament 14. In an exemplary lamp, the centralsection 72 has a coil diameter of about 3 mm to 4 mm and coil spacing ofabout 0.2 mm; however, the skilled artisan can readily apply theteachings herein to filaments of other dimensions. As best seen fromFIG. 8, the length of the expansion compensation section 74, as measuredalong the filament axis, is small compared to the length of the centralsection 72, preferably representing less than about one tenth of thecentral section 72, but each expansion compensation section 74preferably includes at least 2.5 turns or windings.

[0039] The illustrated expansion compensation section 74 comprisesintegral coils formed from the same wire as the main heater coils in thecentral section 72 of the filament 14. Advantageously, no additionalparts are required to implement the expansion sections 74; the formationof windings is simply adapted to include coils of a larger diameter andlower pitch (greater spacing) at the lateral ends of the filament 14.The skilled artisan will readily appreciate in view of the presentdisclosure, however, that similar functionality can be obtained withseparately formed elements bonded to either end of the filament 14.Furthermore, such elements need not necessarily comprise coils but cancomprise other devices capable of readily compressing in response tothermal expansion of the filament 14, and also capable of carryingcurrent to the filament 14. Other examples of expansion compensationdevices include leaf springs, memory metals in readily compressibleconfigurations, etc.

[0040]FIG. 8 illustrates the operation of the preferred embodiment inaccordance with the present invention. As current passes through thefilament 14, the central portion 72 of the filament 14 expands (marked“thermal expansion” in FIG. 8). Preferably, as measured lengthwise, thecentral portion 72 comprises at least 70% of the filament 14, morepreferably, 80% of the filament 14, and most preferably, 90% of thefilament 14. The expansion of the filament 14 causes the expansioncompensation sections 74 on either end of the filament 14 to becompressed, as is illustrated in the section marked “compression.”Advantageously, the expansion compensation sections 74 allow thefilament 14 to expand while heating, and contract while cooling, therebyallowing the filament 14 to retain its original shape. Preferably, afterrepeated cycling (at least 2,000 cycles), the filament returns to lessthan 101.5% of its original length, more preferably, 101% of itsoriginal length, and most preferably, 100.5% of its original length.Advantageously, the coils of the filament are prevented from shorting,and lamp life is increased.

[0041] It will be appreciated by those skilled in the art that variousmodifications and changes may be made without departing from the scopeof the invention. Such modifications and changes are intended to fallwithin the scope of the invention, as defined by the appended claims.

I claim:
 1. A lamp, comprising: a transparent sleeve having an innersurface with an inner diameter D; a filament housed within and extendingaxially along the transparent sleeve; and a plurality of filamentsupports for radially spacing the filament from the inner surface of thetransparent sleeve, the filament supports including a plurality ofaxially spaced pairs of sleeve-contacting portions, wherein adjacentsleeve-contacting portions of the pairs are axially spaced by a distanceL, and a ratio of L/D for each pair is between about 0.5 and 1.25. 2.The lamp of claim 1, wherein the ratio of L/ID for each pair is betweenabout 0.7 and 1.1.
 3. The lamp of claim 2, wherein the ratio of L/D foreach pair is about 1.0.
 4. The lamp of claim 1, wherein thesleeve-contacting portions of each pair are connected to one another. 5.The lamp of claim 4, wherein the sleeve-contacting portions are sized toclosely conform to the inner surface of the transparent sleeve, eachfilament support further comprising a smaller inner portion sized toclosely conform to an outer surface of the filament.
 4. The lamp ofclaim 5, wherein the filament comprises a wire coil and the innerportion of each filament support closely conforms to the outer surfaceof the coiled wire.
 5. The lamp of claim 4, wherein each filamentsupport comprises two conical spirals joined at their apexes, thesleeve-contacting portions formed by outer winds of the conical spirals.6. The lamp of claim 4, wherein each filament support resembles theletter “H” when viewed from the side.
 7. The lamp of claim 4, whereineach filament support resembles the letter “X” when viewed from theside.
 8. The lamp of claim 1, wherein the filament is suspended betweena pair of expansion compensation sections proximate lateral ends of thefilament, the expansion compensation sections being more readilycompressible than the coil of the central section without shorting. 9.The lamp of claim 1, having a maximum capacity of greater than about 1kW.
 10. The lamp of claim 1, having a maximum capacity of greater thanabout 3 kW.
 11. The lamp of claim 1, having a maximum capacity ofgreater than about 6 kW.
 12. The lamp of claim 1, having a maximumcapacity of greater than about 10 kW.
 13. A lamp having a maximumcapacity of at least about 1 kW, the lamp comprising: a transparentsleeve; a filament extending between electrodes and through thetransparent sleeve; at least one filament support comprising: a firstsleeve-contacting portion; a second sleeve-contacting portion spacedfrom the second sleeve-contacting portion; and a filament-contactingportion connected to the first and second sleeve-contacting portions.14. The lamp of claim 13, wherein the filament-contacting portion isinterposed between the first and second sleeve-contacting portions. 15.The lamp of claim 13, wherein the filament comprises a wire coil and thefilament-contacting portion of the filament support closely conforms toan outer surface of the coiled wire.
 16. The lamp of claim 13, whereinthe filament support comprises two spirals, the sleeve-contactingportions formed by outer winds of the spirals.
 17. The lamp of claim 16,wherein the spirals comprise conical spirals tapering from thesleeve-contacting portions.
 18. The lamp of claim 17, wherein spiralsare joined near their apexes to form the filament-contacting portion.19. The lamp of claim 13, wherein the transparent sleeve has an innerdiameter D, the sleeve-contacting portions of the filament support areaxially spaced from one another by a distance L, and a ratio of L/D forthe filament support is between about 0.5 and 1.25.
 20. The lamp ofclaim 19, wherein the ratio of L/D is between about 0.7 and 1.1.
 21. Thelamp of claim 13, comprising a plurality of axially spaced filamentsupports.
 21. A filament support for radially spacing a lamp filamentfrom a transparent sleeve, the filament support comprising: a firstsleeve-contacting portion; a second sleeve-contacting portion spacedfrom the second sleeve-contacting portion; and a filament-contactingportion connected to the first and second sleeve-contacting portions.22. The filament support of claim 21, comprising two conical spiralsjoined at their apexes, the sleeve-contacting portions formed by outerwinds of the conical spirals.
 23. The filament support of claim 21,wherein the filament-contacting portion is interposed between the firstand second sleeve-contacting portions.
 24. The filament support of claim13, wherein the sleeve-contacting portions have an outer diameter D andare axially spaced from one another by a distance L, a ratio of L/Dbeing between about 0.5 and 1.25.
 25. The filament support of claim 24,wherein the ratio of L/D is between about 0.7 and 1.1.